Added support for createPattern; only works with POT textures
Remember texture params when binding
Draw pattern as multiple quads; works correctly in all(?) cases
Release fillPattern
Draw patterns in fragment shader
Cleaned up shaders
Create offscreen canvas with backingStoreRatio 2 by default
Added getImageDataHD/putImageDataHD
Removed createPattern from TODO
Added CanvasPattern; close #48
Cosmetics